This invention relates to mounts for replaceable ink jet heads and, more particularly, to a new and improved ink jet head mount requiring less retention force.
In an ink jet head mounting arrangement, it is necessary to position the ink jet head precisely at a required location in a carriage which conveys the head adjacent to a substrate to be printed with ink from the head in order to assure correct printing. The retention force applied to the head to retain it in position in the carriage must be adequate to keep the head from moving or shifting under vibration, shock and acceleration forces during scanning of the head adjacent to the substrate. In addition, it is necessary to make electrical connections to the ink jet head to supply actuating signals to electromechanical ink drop ejectors and, moreover, it may also be necessary to provide fluid connections to supply ink and/or air to the ink jet head.
For rapid installation and removal of a replaceable ink jet head in a carriage, the retention device may be a handle arrangement which applies force to the ink jet head to urge it against mounting pads which locate the replaceable head in the desired position in the carriage and also against electrical contact pads through which signals are supplied to the ink jet head. A typical prior art arrangement is illustrated in FIG. 1, in which an ink jet head 10 from which ink drops 11 are selectively ejected from orifices 12 toward an adjacent substrate 13 supported on a platen 14. The ink jet head 10 is removably mounted on a carriage 15 which is guided on a bar 16 for reciprocal motion perpendicular to the plane of the drawing. In order to position the head 10 properly on the carriage 15, the head and carriage are provided with front-facing mounting pads 17 on the front surface of the head and rear-facing mounting pads 18 on an opposed surface of the carriage, which are urged into engagement by a locking handle 19 applying a forwardly-directed force to the rear surface 20 of the ink jet head.
In order to transmit electrical signals to a series of transducers 21, which are arranged to selectively eject the ink drops 11 from the series of orifices 12, the transducers are connected through corresponding wires 22 to a series of spring contacts 23 arrayed on the front surface of the head and a corresponding series of spring contacts 24 is positioned in the adjacent surface of the carriage 15 and connected to corresponding conductors 25 leading to a control unit (not shown) in which the actuating signals are generated.
With this conventional replaceable ink jet head mounting arrangement, the force applied to the head 10 by the handle 19 must be greater than the sum of the spring forces produced by the series of contacts 23 and 24 and the acceleration and shock forces which tend to separate the surfaces 17 and 18 when the ink jet head 10 is accelerated and stopped in either direction during its reciprocal motion. For example, if each spring contact combination 23 and 24 requires a force of 5 grams in order to assure proper engagement, and there are 32 ink jets in the ink jet head, the total force required to assure contact for the entire series of 32 contacts is 160 grams. Moreover, if the ink jet head 10 weighs 50 grams and is subjected to 5 G's during acceleration and stopping, then the mounting force required to maintain the head in the desired position during operation is at least 250 grams. Consequently, a total of more than 400 grams of force must be applied by the handle 19 to hold the head in the desired position.
Furthermore, if the number of jets in the ink jet head is increased, the total force required can be substantially greater. For example, if there are 96 jets in the ink jet head 10, and the spring contacts require 5 grams each to force them into the engagement position, the total required electrical contact force will be about 500 grams or more. With more jets, the head will be larger and contain more ink weighing, for example, 100 grams, which requires a head mounting force of at least 500 grams to withstand a 5 G acceleration force, so that a total force of at least 1,000 grams must be applied by the handle 19 to the rear surface 20 of the head.